The present invention relates to the field of sheaths for introducing intravascular catheters. In particular, the present invention relates to a flexible sheath for percutaneously introducing intravascular catheters such as an angioplasty catheter.
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating various types of vascular diseases. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of an introducer sheath positioned at the entry point of the intravascular catheters into the cardiovascular system. For instance, the distal end of the introducer sheath is inserted into the femoral artery located in the groin of the patient and pushed distally through the artery until the sheath is firmly seated within the artery. The proximal end of the introducer sheath protrudes outside of the patient's body to provide an entryway for subsequent insertion of additional or other intravascular devices. The additional or other intravascular devices include guide catheters, guide wires, and balloon dilatation catheters, or angiographic catheters as well as other therapeutic and diagnostic intravascular catheters.
The introducer sheath typically is inserted into the vessel through the skin percutaneously. Prior to the development of percutaneous insertion method, entry into the vessel was achieved by cutting the skin with a scalpel to expose the vessel of interest and then inserting a needle or other puncture apparatus through the vessel wall to facilitate entry of the introducer sheath and/or an intravascular catheter. In the percutaneous insertion technique, a needle or similar puncture device is inserted into the skin without first cutting the skin to expose the vessel. The needle is then advanced through the skin (and tissue) until the needle enters the vessel of interest.
In the common percutaneous insertion procedure, a distal end of a hollow thin-walled puncture needle (alternatively, a Seldinger needle may be used) is inserted through the skin (and underlying tissue) and through a wall of the desired vessel. A proximal end of the needle remains outside of the surface of the skin. Next, a distal end of a thin flexible wire is inserted into the proximal end of the needle and advanced therethrough until a distal end of the wire extends distally beyond the distal end of the needle and into the vessel. A proximal end of the wire remains outside, extending through the proximal end of the needle. While maintaining the flexible wire in position within the vessel, the needle is proximally withdrawn over the wire until completely removed from the vessel and the skin (and underlying tissue).
Next, the physician prepares an introducer sheath outside the patient's body by inserting a distal end of a dilator (e.g., an elongate flexible cylinder with a bore extending therethrough) into a proximal end of the flexible plastic introducer sheath and advances the dilator therethrough. The dilator is advanced until a distal tip portion of the dilator extends distally beyond a distal end of the sheath and a proximal portion of the dilator remains outside of the proximal end of the sheath. The distal tip portion of the dilator has a tapered outer diameter that gradually increases proximally to an enlarged diameter adjacent the distal end of the sheath. By means of a snap fit or friction fit, the proximal portion of the dilator is releasably secured to the proximal portion of the sheath so that the dilator and sheath comprise an assembled unit for insertion into the vessel.
The distal end of the dilator (with the sheath loaded thereon) is threaded over the proximal end of the wire and inserted through the skin (and underlying tissue) and into the vessel by distally advancing the dilator and sheath over the wire. Because the dilator is longer than the sheath, the distal end of the dilator enters the vessel before the distal end of the sheath and the dilator and sheath are advanced together until the distal portion of the sheath extends within the vessel. The tapered distal tip portion of the dilator gradually expands the opening in the vessel wall as the dilator moves there through. With the distal end of the sheath properly positioned (extending into the vessel), the proximal end of the sheath and the proximal end of the dilator remain outside the surface of the skin. Next, while maintaining the sheath in place within the vessel and after disengaging the dilator from the sheath, the dilator and wire are removed by proximally withdrawing them from inside the sheath. With the sheath in place, the puncture site is now ready for the widely known transluminal angioplasty procedure or other procedure involving intravascular catheters. The sheath provides a convenient and protective entryway for intravascular devices into the cardiovascular system.
In the case of an angioplasty procedure, the next step includes inserting a distal end of a hollow guide catheter through the sheath and into the vessel. A proximal end of the guide catheter remains outside of the proximal end of the sheath for facilitating insertion of intravascular devices through the guide catheter. For instance, a guide wire could be inserted through the guide catheter and advanced distally until a distal end of the guide wire is distal to a stenosis in a coronary artery. A balloon dilatation catheter is then threaded over the proximal end of the guide wire and inserted up through the guide catheter and manipulated to treat a stenosis.
The sheath for introducing the guide catheter and other intravascular devices facilitates the insertion and withdrawal of intravascular devices through the skin and underlying tissue into a vessel. The sheath minimizes trauma to the skin puncture site and vessel wall caused by the frequent insertion and removal of intravascular devices from the vessel. In addition, the introducer sheath prevents backbleeding, i.e., blood flow exiting the punctured vessel, because the typical sheath has a hemostasis valve carried therein at its proximal end. The hemostasis valve forms a fluid tight seal about a variety of sizes of intravascular catheters, guide wires, and the like to prevent a flow of blood out of the patient or air into the patient. The hemostasis valve also sealingly closes when no device extends through the hemostasis valve (and sheath).
Although the inner diameter of the sheath should have a close tolerance with the outer diameter of the intravascular device, it is desirable to have some spacing between the sheath and intravascular device for perfusion or for drug infusion flow techniques through that spacing. A side arm with a 3-way valve connector connected to the proximal end or hub of the sheath can be used for blood perfusion or drug infusion.
Reasons for minimizing the size of a sheath include minimizing the size of the opening in the vessel and the skin puncture site, increasing the stability of the sheath within the skin puncture site, and reducing the time for this puncture site to heal. There are two reasons that this time is of interest. First, ensuring the proper clotting of this opening requires the attention of trained personnel for several minutes (e.g., 15 minutes) after the sheath is removed. Second, patients need to remain immobile for many hours after the sheath is removed to ensure that the clotted opening in the vessel does not reopen. These healing times are so long because patients typically have Heparin.RTM., an anticoagulant, in their cardiovascular systems. It is desirable to reduce both of these times.
Although it is desirable to minimize the outer diameter of the introducer sheath, an intravascular device having an outer diameter larger than the inner diameter of the introducer sheath already in place may be required later in the surgical procedure. These larger size intravascular devices require the use of a larger size introducer sheath and accordingly, necessitate exchanging the first introducer sheath for another introducer sheath having a larger inner diameter.
For example, this situation frequently arises because a smaller size introducer sheath is required for angiography procedures and a larger size introducer sheath is required for an angioplasty procedure. For example, a procedure using angiography catheters typically would be performed with an introducer sheath having a size 5 or 6 French inner diameter. However, present day angioplasty guide catheters (through which a angioplasty dilation catheter would pass) are generally too large to fit through size 5 and 6 French introducer sheaths. Accordingly, if it were determined that an angioplasty procedure were required, then a larger inner diameter size introducer sheath (e.g., 7 or 8 French) would be needed to accommodate the outer diameter of an angioplasty guide catheter. If an adjunctive procedure such as an atherectomy or stent placement procedure would be necessary after or instead of the angioplasty procedure, an even larger size introducer sheath would be required.
With the possibility of these different sized introducer sheaths being required, the physician is faced with a dilemma. It is highly desirable to use the smallest size introducer sheath possible to minimize the size of the opening in the skin and in the vessel (e.g., femoral artery). However, if one selects an introducer sheath that is too small to accommodate all the necessary intravascular devices, then the smaller size introducer sheath would have to be later exchanged for a larger one. Confronted by this choice, physicians commonly choose to insert an introducer sheath of a size large enough to easily accommodate all potential intravascular devices. This means that an introducer sheath frequently is selected that is much larger than necessary and this initial choice for the larger introducer sheath may sacrifice the highly desirable goal of minimizing the size of the opening in the artery wall and skin puncture site.
In a case where a smaller inner diameter size sheath was initially selected and must be removed to be replaced by a larger inner diameter size sheath, all intravascular devices from within the vessel typically must be removed (with the possible exception of a coronary guide wire). Next, the smaller size sheath must be removed from the vessel and skin surface puncture site. To do so, with the sheath still in place within the vessel, the physician reinserts the dilator into the sheath until the dilator extends within the vessel beyond the sheath (and the sheath locks with the dilator) so that the wire may be threaded through the dilator until the distal end of the wire extends through the vessel distally beyond the distal end of the dilator. While leaving the wire in place within the vessel, the dilator and sheath are removed from within the vessel.
Next, to place a larger introducer sheath within the vessel, a physician would repeat the entire percutaneous puncture insertion method for introducer sheaths as previously described (except for not using a puncture needle because the wire already extends the vessel). If this procedure is performed at a new puncture site along the vessel, then a new puncture site would be needed. In any case, repeating the percutaneous insertion procedure traumatizes the endothelium layer of the vessel wall, the surrounding tissue, and the skin much more than performing the percutaneous insertion technique only once. Moreover, many patients receiving angioplasty treatment already suffer from diseased arterial walls which magnifies the problem of repetitious trauma to vessel wall.
Because of the large number of devices of varying sizes which may be used in a combined angiography/angioplasty, or adjunctive procedure, the conventional introducer sheath has many deficiencies. One major deficiency is that there is no mechanism for increasing the size of the introducer sheath (once having been inserted) other than by replacing the smaller size introducer sheath with a second larger size introducer sheath through a second percutaneous insertion procedure. This deficiency drives the physician to reluctantly select an introducer sheath with a size potentially much larger than necessary, needlessly increasing the size and healing time of the opening created in the vessel wall and skin surface. This results, in substantial part, in increased patient recuperation time which typically dictates an overnight stay in the hospital for a procedure that otherwise could be done on an outpatient basis.
Various attempts have been made at solving the problem of having an expandable or variable size introducer device. For example, Grayzel U.S. Pat. No. 4,921,479 is directed to a removable, expandable sheath for introducing catheters. The sheath is made of a semi-stiff plastic with memory and formed in a tubular configuration with a longitudinal slit extending along the entire length of the sheath. The tubular structure is typically coiled about its longitudinal axis so its tubular wall overlaps itself. Upon insertion of a larger diameter intravascular device, the tubular sheath enlarges its inner diameter by uncoiling to the extent necessary to accommodate the catheter inserted therein. The Grayzel device is disadvantageous because the slit extending the length of the sheath permits potential backbleeding and the moveable nature of the walls relative to each other can traumatize the vessel possibly causing a dissection of the vessel wall or at least exacerbating the injury to the endothelium lager of the vessel wall and the skin tissue.
Another attempt includes Schreck U.S. Pat. No. 4,411,655 which relates to an expandable cannula for introducing catheters into the cardiovascular system. The cannula is made of a metallic shape-memory alloy formed into a cylindrical cannula with a plastic sheath covering the cannula. The lumenal diameter of the cannula dilates after insertion into the body vessel as the temperature of the shape-memory alloy is heated by equilibrating to the predetermined body temperature or by application of resistance heating or other methods to activate the shape-memory alloy. This device requires an additional plastic sheath to the cover metal alloy cannula, thereby creating an outer diameter larger than necessary. Moreover, because the cannula is made of a metal alloy, it is inflexible contributing to greater tissue trauma because the cannula will have less "give" when pressing against the surrounding tissue and vessel wall. Moreover, in the embodiment in which the cannula expands because of the temperature of the body, there is no choice for the operator to decide when the cannula expands.